Question: What is the proportion for potassium-40 before it decays to argon-40?
Paraphrase: What is the amount of potassium-40 before it decays into argon-40?
SPARQL (Wikidata): SELECT ?value WHERE { wd:Q2251076 p:P816 ?s . ?s ps:P816 wd:Q1929004 . ?s pq:P1107 ?value}